Massachusetts
particularly Cape Cod and the Islands or Cape Ann and the North Coast north of Boston. You can't go wrong with Mass. It's an awesome place esp. if you are going anytime in the summer. Dozens of beautiful beaches, historic towns, shopping, eating out, touring, biking, water-skiing, fishing/boating or just lounging on the beach, it's great. There's so much to see and do there. I personally am dying to go sometime this summer. The scenery and views in the area are worth the trip alone. The Cape also has bike trails through a majority of it and a National Seashore near the end. There are a plethora of bed/breakfasts, hotels, motels and even a few hostels to stay in. Also, if you have the time and can fit it in your budget, you should definitely visit either Martha's Vineyard or Nantucket or both. They are islands and are well worth the trip. There are several ferries that run between quaint seaside towns like Falmouth and Woods Hole that go back and forth between them and the mainland, perfect for day trips. A hint if you are planning to go in the high summer season is to pick a spot out of the way to stay, because it gets quite crowded in this area. Also, plan your trip in advance and make a short list of desired stops on your itinerary. You'll see lighthouses, antique ships, quaint old towns, cobbled streets, and I hope you like lobster! there's lots of it, the local specialty. Another place I recommend visiting is Newport, Rhode Island. One of the most beautiful small towns in the US and very historic, located right on the bay is about as good as it gets. A must see/do in Newport is the Cliff Walk at The Breakers, which is right on the water and offers spectacular views of the ocean and the famous Newport Mansions.
I would recommend any/all of these places for a wonderful vacation:
1. Cape Cod
2. Martha's Vineyard
3. Nantucket
4. Cape Ann
5. Newport, RI